Inputs:
filterSpec - similar to uigetfile's filterSpec. Examples:
'defaultFile.mat'
'*.mat'
{'MAT files', '*.mat'}
{'Data or m files (*.m,*.mat)', {'m';'mat'}}
prompt - optional dialog prompt (default: 'Select file')
folder - optional default folder (default: current folder)
callback - optional handle to a callback function with the following interface:
callbackFunction(hPanel, filename)
The callback function should check the specified file and update the specified panel accordingly.
(default: [])
multiSelect - optional flag specifying whether multiple files can be selected (default: false)

Output:
filename - full-path filename of the selected file(s) (or empty array)

Warning:
This code heavily relies on undocumented and unsupported Matlab functionality. It is expected to work on Matlab 7.4+, but use at your own risk!

Bugs and suggestions:
Please send to Yair Altman (altmany at gmail dot com)